25-Hydroxyvitamin D in obese youth across the spectrum of glucose tolerance from normal to prediabetes to type 2 diabetes

Serum 25-Hydroxyvitamin D Levels and Youth-Onset Type 2 Diabetes: A Two-Sample Mendelian Randomization Study

Observational studies have linked vitamin D insufficiency to pediatric type 2 diabetes (T2D), but evidence from vitamin D supplementation trials is sparse. Given the rising prevalence of pediatric T2D in all ethnicities, determining the protective role of vitamin D has significant public health importance. We tested whether serum 25-hydroxyvitamin D (25OHD) levels are causally linked to youth-onset T2D risk using Mendelian randomization (MR). We selected 54 single-nucleotide polymorphisms (SNPs) associated with 25OHD in a European genome-wide association study (GWAS) on 443,734 individuals and obtained their effects on pediatric T2D from the multi-ethnic PRODIGY GWAS (3006 cases/6061 controls). We applied inverse variance weighted (IVW) MR and a series of MR methods to control for pleiotropy. We undertook sensitivity analyses in ethnic sub-cohorts of PRODIGY, using SNPs in core vitamin D genes or ancestry-informed 25OHD SNPs. Multivariable MR accounted for the mediating effects of body mass index. We found that a standard deviation increase in 25OHD in the logarithmic scale did not affect youth-onset T2D risk (IVW MR odds ratio (OR) = 1.04, 95% CI = 0.96-1.13, p = 0.35) in the multi-ethnic analysis, and sensitivity, ancestry-specific and multivariable MR analyses showed consistent results. Our study had limited power to detect small/moderate effects of 25OHD (OR of pediatric T2D < 1.39 to 2.1). In conclusion, 25OHD levels are unlikely to have significant effects on the risk of youth-onset T2D across different ethnicities.

Vitamin D deficiency and cardiometabolic risk factors in adolescents: systematic review and meta-analysis

Vitamin D deficiency is associated with an increase in the occurrence of cardiometabolic events, but the evidence of this relationship in adolescence is still limited. Thus, we analyzed the association between vitamin D deficiency and cardiometabolic risk factors in adolescents. Observational studies were searching in PubMed/Medline, Embase, Scopus, Web of Science, Science Direct, Lilacs, and Google Scholar database. Random effects models were used to summarize standardized mean differences for as a summary measure. The certainty of the evidence was verified using the Cochrane recommendations. A total of 7537 studies were identified, of which 32 were included in the systematic review and 24 in the meta-analysis.Vitamin D deficiency was associated with increased systolic pressure (SMD = 0.22; 95%CI = 0.10; 0.34), diastolic pressure (SMD = 0.23; 95%CI = 0.10; 0.35), glycemia (SMD = 0.13; 95%CI = 0.05; 0.12), and insulin (SMD = 0.50; 95%CI = 0.15; 0.84), an increase in the HOMA index (SMD = 0.48; 95%CI = 0.36; 0.60), high triglyceride values (SMD = 0.30; 95%CI = 0.11; 0.49), and reduced HDL concentrations (SMD= -0.25; 95%CI = -0.46; -0.04). No statistically significant association was observed for glycated hemoglobin, LDL cholesterol, and total cholesterol. Most of the studies presented low and moderate risks of bias, respectively. The certainty of the evidence was very low for all the outcomes analyzed. Vitamin D deficiency was associated with increased exposure to the factors linked to the occurrence of cardiometabolic diseases in adolescents. Systematic Review Registration: PROSPERO (record number 42,018,086,298).

Prevalence of Vitamin D Deficiency and Its Association with Insulin Resistance in Obese Women with Normal Fasting Glucose

Results

A total of 264 obese and 133 normal BMI women (controls) of age range 20-50 years were selected. Obese women had significantly lower vitamin D compared to control women (P < 0.05). Among euglycemic (fasting glucose < 100 mg/dl) obese women (n = 221), 90 (40.7%) were vitamin D deficient. Serum PTH and calcium levels were negatively correlated, though nonsignificantly with vitamin D (r = −0.172, P = 0.090, and r = −0.051, P = 0.557, respectively). The mean age, BMI, waist circumference (WC), hip circumference (HC), waist-to-hip ratio (WHR), fasting glucose, fasting insulin, PTH, and calcium were not significantly different in vitamin D-deficient as compared to nondeficient obese women. IR was detected in 109 (49.3%) obese women. Mean HOMA-IR in vitamin D-deficient women was significantly higher than that in the nondeficient obese women (3.03 ± 1.64 vs. 2.40 ± 1.02; P = 0.041), but the percentage of women with IR was comparable in both groups (51.1% vs. 45.8%; P = 0.745). Univariate analysis revealed that HOMA-IR was negatively correlated with vitamin D and positively with BMI and PTH. A multivariate regression analysis, stepwise method revealed that BMI and PTH were independent determinants of HOMA-IR instead of vitamin D.

Conclusion

More than 40% of obese women were vitamin D deficient. Among euglycemic obese women, 49% were insulin resistant. Prevalence of insulin resistance, though negatively correlated with vitamin D, could be better explained by BMI and PTH levels.

Insulin Resistance Is Inversely Associated with the Status of Vitamin D in Both Diabetic and Non-Diabetic Populations

Vitamin D has been implicated in the regulation of glucose metabolism and insulin resistance. We designed this study to provide evidence that insulin resistance is dependent on the concentration of vitamin D in the body. Forty observational studies of both type 2 diabetes mellitus patients and healthy subjects were included in this meta-analysis. Related articles were searched from Embase, PubMed, and Medline through January 2021. Filters for search were used to obtain more focused results. We used Comprehensive Meta-Analysis Version 3 for the construction of forest plots. RevMan software version 5.3 was used to build the risk of bias tables and summary plots. The observational studies included in this systematic review and meta-analysis showed an inverse relationship of insulin resistance with the status of vitamin D both in non-diabetic (r = -0.188; 95% CI = -0.141 to -0.234; p = 0.000) and diabetic (r = -0.255; 95% CI = -0.392 to -0.107, p = 0.001) populations. From the meta-analysis we concluded that hypovitaminosis D is related to increased levels of insulin resistance in both type 2 diabetes patients and the healthy population all over the world.

No association of 25-hydroxyvitamin D and parathormone levels with glucose homeostasis in type 2 diabetes - a study from Shillong, Meghalaya

Background: Although inadequate vitamin D and altered parathyroid hormone (PTH) are implicated in deranged glucose metabolism and risk of future diabetes, their role in regulating glucose homeostasis in established cases of diabetes is unclear. We aimed to (i) evaluate vitamin D status, and (ii) determine if vitamin D and PTH were associated with parameters of glucose homeostasis in type 2 diabetes (T2D) patients from Meghalaya, India. Methods: We determined 25-hydroxyvitamin D (25-OH-D) and PTH concentrations in 251 T2D patients (not on insulin), and examined their associations with the following parameters of glucose homeostasis: fasting blood sugar (FBS), post-prandial blood sugar (PPBS), glycated hemoglobin (HbA1c), fasting insulin (FI), homeostasis model assessments of insulin resistance (HOMA-IR) and β-cell function (HOMA-β). Results: None of the patients had adequate vitamin D (mean 25-OH-D = 19.3 ng/mL); 47.8% patients were deficient (25-OH-D < 20 ng/mL), while 52.2% were insufficient (25-OH-D < 30 ng/mL) vitamin D. Significant (P < 0.05) univariate associations were observed between: 25-OH-D and FI (r = 0.14); 25-OH-D and HOMA-β (r = 0.13); PTH and FI (r = -0.18), and PTH and HOMA-β (r = -0.11). However these associations disappeared after controlling for potential confounders. The 25-OH-D and PTH levels were not associated with any of the tested parameters of glucose homeostasis. Conclusion: There was widespread prevalence of vitamin D deficiency/insufficiency in our sample T2D patients. However, neither vitamin D nor PTH appeared to play a major role in influencing glucose homeostasis in this present selection of T2D cases.

Comprehensive Review on Diabetes Associated Cardiovascular Complications - The Vitamin D Perspective

Vitamin D, a steroid hormone is primarily known for its role in calcium and bone mineral homeostasis. Over the years, vitamin D has been implicated in various non-skeletal diseases. The extraskeletal phenomenon can be attributed to the presence of vitamin D receptors (VDRs) in almost all cells and identification of 1-α hydroxylase in extrarenal tissues. The vitamin D deficiency (VDD) pandemic was globally reported with increasing evidence and paralleled the prevalence of diabetes, obesity and cardiovascular diseases (CVDs). A dependent link was proposed between hypovitaminosis D glycemic status, insulin resistance and also the other major factors associated with type 2 diabetes leading to CVDs. Insulin resistance plays a central role in both type 2 diabetes and insulin resistance syndrome. These 2 disorders are associated with distinct etiologies including hypertension, atherogenic dyslipidemia, and significant vascular abnormalities that could lead to endothelial dysfunction. Evidence from randomised clinical trials and meta-analysis, however, yielded conflicting results. This review summarizes the role of vitamin D in the regulation of glucose homeostasis with an emphasis on insulin resistance, blood pressure, dyslipidaemia, endothelial dysfunction and related cardiovascular diseases and also underline the plausible mechanisms for all the documented effects.

Vitamin D and the paraventricular nucleus: Relevance for type 2 diabetes

Vitamin D deficiency is linked to type 2 diabetes and we recently showed this may be through action of vitamin D in the paraventricular nuclei (PVN) in the hypothalamus of the brain. This review focuses on the known roles of the PVN in glucose control and how previously discovered actions of vitamin D in other tissues may translate to action in the PVN. Specifically, we focus on the role of insulin and inflammation in the hypothalamus and how these may be modified through vitamin D action.

Is Hypovitaminosis D Related to Incidence of Type 2 Diabetes and High Fasting Glucose Level in Healthy Subjects: A Systematic Review and Meta-Analysis of Observational Studies

There is evidence that vitamin D status is associated with type 2 diabetes. Many observational studies have been performed investigating the relationship of vitamin D status and circulating biomarkers of glycemic regulation. To find out whether this association holds, we conducted a systematic review and meta-analysis of cross sectional and longitudinal studies. We searched Pubmed, Medline and Embase, all through June 2017. The studies were selected to determine the effect of vitamin D on the parameters of glucose metabolism in diabetic and non-diabetic subjects. Correlation coefficients from all studies were pooled in a random effects meta-analysis. The risk of bias was assessed using Grading of Recommendations Assessment, Development and Evaluation (GRADE) system. We found significant inverse relationship of vitamin D status with glycemic level in both diabetic (r = -0.223, 95% CI = -0.184 to -0.261, p = 0.000) and non-diabetic (r = -0.073, 95% CI = -0.052 to -0.093, p = 0.000) subjects. This meta-analysis concludes that hypovitaminosis D is associated with increased risk of hyperglycemia both in diabetic and non-diabetic subjects. A future strategy for the prevention of impaired glycemic regulation could be individualized supplementation of vitamin D.

Race or vitamin D: A determinant of intima media thickness in obese adolescents?

OBJECTIVE

Carotid intima media thickness (IMT), a predictor of cardiovascular events, is reported to be higher in African-American (AA) vs White (AW) individuals. We investigated whether racial differences in IMT in obese adolescents could be explained by differences in 25 hydroxy-vitamin D [25(OH)D].

RESEARCH DESIGN AND METHODS

A total of 63 obese adolescents had 25(OH)D levels, determination of IMT, body composition, insulin sensitivity (IS) by hyperinsulinemic-euglycemic clamp, lipids and blood pressure (BP).

RESULTS

IMT was higher and 25(OH)D lower in AA vs AW. IMT correlated with 25(OH)D level (r = -0.38, P = .002) but not with IS. In multiple regression analysis, race, HbA1c, BP and age, and not 25(OH)D, BMI or IS, were the significant determinants of IMT (R² = 0.44, P < .001). Without race in the model, 25(OH)D (β = -0.36, P = .009) contributed to the variance in IMT (R² = 0.32, P = .007).

CONCLUSION

Obese AA adolescents vs AW, have higher IMT, explained by race, BP, and HbA1c. Although 25(OH)D levels contribute to the variance in IMT, the observed racial difference in IMT could be mediated through other unknown race-related factors besides 25(OH)D.

Obesity Cardiometabolic Comorbidity Prevalence in Children in a Rural Weight-Management Program

This descriptive study examines the prevalence of obesity-related cardiometabolic (CM) risk factors using CM laboratory metrics, in 3 to 19 year olds presenting to a rural American Academy of Pediatrics stage 3 multidisciplinary weight management clinic based on gender, age ranges, and obesity classes. From 2009 to 2016, 382 children (body mass index ≥85th percentile) enrolled. Multiple logistic regression determined the effects of age, gender, or obesity class on CM risk factors. Odds of elevated insulin were more significant in 15 to 19 year olds than in 3 to 5 year olds, or in 6 to 11 year olds. Obesity class III had higher odds than class II, class I, and overweight in having elevated insulin; twice likely than class II for having low high-density lipoprotein; and twice as likely than class I for high triglycerides. Adolescents and obesity class III categories have significant CM risk but the burden in younger and less severe obesity cohorts cannot be underestimated.

Serum adipokines and vitamin D levels in patients with type 1 diabetes mellitus

INTRODUCTION

Adiponectin, leptin and resistin are adipokines that play important roles in the regulation of lipid and carbohydrate metabolism in type 2 diabetes (T2DM). However, their influence in type 1 diabetes mellitus is still unknown. The aim of this study was to measure serum adiponectin, leptin and resistin levels and to investigate their relationships with vitamin D and other clinical and laboratory parameters in patients with type 1 diabetes.

MATERIAL AND METHODS

Fifty subjects with type 1 diabetes and 50 healthy age- and sex-matched subjects were selected from the Endocrinology Outpatient Clinic of Cairo University Pediatrics Hospital. Enzyme-linked immunosorbent assay was used to measure the levels of leptin, adiponectin and resistin. Vitamin D levels were measured using electro-chemiluminescence immunoassay.

RESULTS

There were no significant differences in adiponectin and leptin levels between diabetic and control subjects (p = 0.6 and p = 0.5 respectively). Resistin levels were significantly higher in the diabetic group compared to controls (p < 0.001) and in postpubertal patients compared to prepubertal patients (p < 0.04). Serum resistin in type 1 diabetes showed a negative correlation with vitamin D (p < 0.001) and a positive correlation with glycated hemoglobin (HbA_1c) (p = 0.006), while other adipokines were not interrelated.

CONCLUSIONS

These results strongly support a role of resistin and vitamin D deficiency in the pathophysiology of type 1 diabetes. Vitamin D may be involved in resistin regulation through an unknown mechanism. Further studies are recommended to understand resistin regulation in type 1 diabetes.

Vitamin D supplementation, the metabolic syndrome and oxidative stress in obese children

BACKGROUND

Previous studies suggest that vitamin D may play a role in cardiovascular and metabolic health. Oxidative stress has also been implicated in the development of cardiovascular disease. Evidence suggests that vitamin D deficiency may contribute to the occurrence of oxidative stress. This study aimed to determine whether treatment and correction of vitamin D deficiency in obese children led to changes in their metabolic profile, independent of changes in adiposity. In addition, we aimed to determine whether vitamin D deficiency and oxidative stress are causally related in obese children.

METHODS

In the retrospective arm, chart review identified 32 obese children who experienced normalization of vitamin D deficiency or insufficiency with vitamin D supplementation. We then correlated laboratory and anthropometric data with vitamin D levels. In the prospective arm of the study, urinary 8-isoprostane and hydrogen peroxide were measured before and after correction of vitamin D deficiency/insufficiency and correlated to vitamin D levels in seven patients.

RESULTS

In our predominantly Hispanic population of obese children in an urban setting, we demonstrated a cause-effect relationship between vitamin D deficiency and oxidative stress. In contrast, we found no association between vitamin D status, adiposity, and markers of insulin sensitivity, nor any effect of vitamin D treatment on the same parameters.

CONCLUSIONS

These discordant findings suggest a differential effect of vitamin D on cardiovascular risk factors such as oxidative stress and insulin resistance. To confirm these findings, further prospective studies with larger sample size and longer follow-up are warranted.

Vitamin D status in youth with type 1 and type 2 diabetes enrolled in the Pediatric Diabetes Consortium (PDC) is not worse than in youth without diabetes

OBJECTIVE

To describe vitamin D levels and prevalence of vitamin D sufficiency, insufficiency and deficiency in a large, ethnically/racially diverse population of youth with type 1 diabetes (T1D) and type 2 diabetes (T2D) in comparison to national data and examine the associations between clinical/demographic factors and vitamin D levels.

METHODS

25-hydroxy vitamin D (25OHD) levels were measured in 215 youth with T1D and 326 youth with T2D enrolled in the Pediatric Diabetes Consortium (PDC). These levels were compared with those of youth of the same age without diabetes from the 2005-2006 NHANES Survey.

RESULTS

Vitamin D deficiency (<21 ng/mL) was present in 36% of PDC participants, and insufficiency (21-29 ng/mL) was present in an additional 34%. About 36% of age-matched youth in the NHANES Survey were vitamin D deficient and an additional 41% were insufficient. Deficiency or insufficiency varied by race/ethnicity, being highest in African-Americans (86%), intermediate in Hispanics (77%), and lowest in non-Hispanic whites (47%). Lower 25OHD levels were observed in African-American and Hispanic youth, during fall and winter, and at sites in the northern United States (all p-values < 0.001). Youth with T2D had significantly lower 25OHD levels than youth with T1D (p < 0.001), but this difference was largely eliminated after adjusting for race/ethnicity and socio-economic status.

CONCLUSIONS

Vitamin D deficiency/insufficiency is present in a substantial proportion of youth with diabetes, particularly minorities, but the prevalence appears similar to that in youth without diabetes. Further studies are needed to examine whether youth with diabetes would benefit from vitamin D supplementation.

Incidence of prediabetes and risk of developing cardiovascular disease in women with polycystic ovary syndrome

Our aim was to determine the incidence of prediabetes and risk of developing cardiovascular disease (CVD) in women with polycystic ovary syndrome (PCOS). This prospective, observational study included 148 women with PCOS, without Type 2 diabetes mellitus (T2DM) and CVD present at baseline. In the fasting blood samples, we measured lipids, glucose, and insulin levels during oral glucose tolerance test, levels of C-reactive protein (CRP), steroids, 25-hydroxyvitamin D (25-OHD), prolactin, thyroid-stimulating hormone, and parathyroid hormone. The follow-up period was 3 years. At baseline, prevalent prediabetes was present in 18 (12%) of PCOS cases and it progressed to T2DM in 5 (3%) of the cases. Incident prediabetes during the follow-up was noted in 47 (32%) women or 4.7 per 1000 persons/year. Prediabetes was associated with elevated body mass index (BMI) (odds ratio [OR] = 1.089, confidence interval [CI]: 1.010; 1.174, p = 0.026), high baseline levels of CRP (OR = 3.286, CI: 1.299; 8.312, p = 0.012), homeostatic model assessment - insulin resistance (IR) (OR = 2.628, CI: 1.535; 4.498, p < 0.001), and high lipid accumulation product (LAP) (OR = 1.009, CI: 1.003; 1.016, p = 0.005). Furthermore, prediabetes was associated with low 25-OHD (OR = 0.795, CI: 0.724; 0.880, p ≤ 0.05). In addition, cardiovascular risk in PCOS women with prediabetes was high (hazard ratio = 1.092, CI: 1.036; 1.128, p < 0.001). We showed association of prediabetes with high BMI, IR, markers of inflammation, LAP, and low serum 25-OHD concentration. IR appears to be more relevant than the other predictors of prediabetes risk in this study. PCOS women are considered as a high-risk population for prediabetes.

Vitamin D deficiency is associated with prediabetes in obese Swedish children

AIM

Low vitamin D levels have been associated with obesity and living in areas that lack sunshine, such as northern Europe. The aim of this study was to investigate the vitamin D status of a group of obese children in Sweden and to investigate the associations between vitamin D status and markers of glucose metabolism and metabolic risk markers.

METHODS

This was a prospective cross-sectional study of 202 obese children between 4.5 and 17.9 years of age who had been referred to the National Childhood Obesity Centre at Karolinska University Hospital, Stockholm. We examined age, gender, 25-hydroxyvitamin D (25(OH)D), f-glucose, f-insulin and metabolic risk markers. Vitamin D deficiency was defined as less than 30 25(OH)D nmol/L. Children with and without a vitamin D deficiency were compared.

RESULTS

Just over a third (33.2%) of our study population had vitamin D levels <30 nmol/L 25(OH)D. A significant interaction effect was found between age and 25(OH)D. An association was also found between low 25(OH)D levels and impaired fasting glycaemia (IFG) independent of age and season.

CONCLUSION

Low vitamin D levels were common among obese adolescents living in Sweden and were strongly associated with age and associated with a higher risk of IFG.

Inverse associations between cardiometabolic risk factors and 25-hydroxyvitamin D in obese American children and adolescents

OBJECTIVES

To examine the association between 25-hydroxyvitamin D [25(OH)D] concentrations and cardiometabolic risk factors in obese American children.

METHODS

A cross-sectional study was conducted on 209 obese children (55% females, 25.8% black) aged between 6 and 19 years old. Study measurements included plasma 25(OH)D concentrations, blood pressure, lipids and oxidized LDL levels, insulin resistance (IR) indices from glucose, insulin and 5 hour oral glucose tolerance test.

RESULTS

Fifty-one percent of the children had vitamin D deficiency. Older age [OR (95% CI) = 1.16 (1.00, 1.35)], black race/ethnicity [15.39 (5.79, 40.92)], winter/spring season [3.46 (1.69, 7.02)] and higher body mass index (BMI) [1.05 (0.99, 1.11)] were associated with increased odds of having vitamin D deficiency. None of cardiometabolic risk factors examined were significantly associated with vitamin D deficiency in age, race/ethnicity, season, and BMI adjusted models. In age, race/ethnicity, season and BMI adjusted models, total cholesterol (β = -0.001, P = 0.013), non-HDL-C (β = -0.001, P = 0.014), and oxidized LDL (β = -0.087, P = 0.045) were inversely associated with log-transformed 25(OH)D. An approximate 10 mg/dl increase in total cholesterol or in non-HDL-C was associated with an approximate 1.3% decrease in the geometric mean of 25(OH)D concentration. Further a 10% increase in ox-LDL levels was associated with an approximate 0.8% decrease in the geometric mean of 25(OH)D.

CONCLUSION

Vitamin D deficiency is prevalent in obese American children. There was evidence that some cardiometabolic risk factors including lipid levels and oxidized LDL levels were significantly inversely associated with 25(OH)D concentration in our sample. Am. J. Hum. Biol. 28:736-742, 2016. © 2016 Wiley Periodicals, Inc.

Vitamin D and insulin resistance

Vitamin D is a steroid hormone, which in active form binds to the vitamin D receptor. Expression of the vitamin D receptor in diverse cell types (pancreatic islet cells, myocytes, hepatocytes and adipocytes) raises the suspicion that vitamin D may be involved in multiple cellular processes, including the response to insulin. Insulin resistance is a characteristic feature of type 2 DM, and its attenuation may reduce the incidence of type 2 DM and cardiovascular disease. In observational studies, low serum 25-hydroxyvitamin D (25-OHD) concentrations are associated with an increased risk of type 2 DM. It has been suggested that increasing serum 25-OHD concentrations may have beneficial effects on glucose and insulin homeostasis. However, cross-sectional and interventional studies of vitamin D supplementation provide conflicting results and demonstrate no clear beneficial effect of vitamin D on insulin resistance. These studies are complicated by inclusion of different patient cohorts, different 25-OHD assays and different doses and preparations of vitamin D. Any possible association may be confounded by alterations in PTH, 1,25-dihydroxyvitamin D or tissue vitamin D concentrations. We identified 39 studies via MEDLINE and PUBMED. We review the evidence from 10 studies (seven observational and three interventional) examining vitamin D and type 2 DM incidence, and 29 studies (one prospective observational, 12 cross-sectional and 16 interventional trials) examining vitamin D and insulin resistance. Based on this data, it is not possible to state that vitamin D supplementation has any effect on type 2 DM incidence or on insulin resistance. Data from the multiple ongoing randomized controlled trials of vitamin D supplementation due to report over the next few years should help to clarify this area.

The Relationship of Serum 25-Hydroxyvitamin D and Insulin Resistance among Nondiabetic Canadians: A Longitudinal Analysis of Participants of a Preventive Health Program

Observational and intervention studies have revealed inconsistent findings with respect to the relationship between vitamin D and insulin resistance. No intervention studies have been conducted in community samples whereas this may be particularly relevant to the primary prevention of type 2 diabetes (T2D) and cardiovascular disease (CVD). In the present study we examined whether temporal improvements in vitamin D status, measured as serum 25-hydroxyvitamin D [25(OH)D], reduce the risk of insulin resistance among individuals without T2D. We accessed and analyzed data from 5730 nondiabetic participants with repeated measures of serum 25(OH)D who enrolled in a preventive health program. We used the homeostatic model assessment for insulin resistance (HOMA-IR) and applied logistic regression to quantify the independent contribution of baseline serum 25(OH)D and temporal increases in 25(OH)D on HOMA-IR. The median time between baseline and follow up was 1.1 year. On average serum 25(OH)D concentrations increased from 89 nanomoles per liter (nmol/L) at baseline to 122 nmol/L at follow up. Univariate analyses showed that relative to participants with baseline serum 25(OH)D less than 50 nmol/L, participants with baseline concentrations of “50-<75”, “75-<100”, “100-<125”, and ≥125 nmol/L were 0.76 (95% confidence intervals: 0.61–0.95), 0.54 (0.43–0.69), 0.48 (0.36–0.64) and 0.36 (0.27–0.49) times as likely to have insulin resistance at follow up, respectively. More importantly, relative to participants without temporal increases in 25(OH)D, those with increases in serum 25(OH)D of “<25”, “25-<50”, “50-<75”, “≥75” nmol/L were 0.92 (0.72–1.17), 0.86 (0.65–1.13), 0.66 (0.47–0.93), and 0.74 (0.55–0.99) times as likely to have insulin resistance at follow up, respectively. In the subgroup of participants without insulin resistance at baseline, this was 0.96 (0.72–1.27), 0.78 (0.56–1.10), 0.66 (0.44–0.99), and 0.67 (0.48–0.94), respectively. These observations suggest that improvements in vitamin D status reduce the risk for insulin resistance and herewith may contribute to the primary prevention of T2D and CVD.

Beta Cell Function and the Nutritional State: Dietary Factors that Influence Insulin Secretion

Approximately 366 million people worldwide have been diagnosed with type-2 diabetes (T2D). Chronic insulin resistance, decreased functional β-cell mass, and elevated blood glucose are defining characteristics of T2D. Great advances have been made in understanding the pathogenesis of T2D with respect to the effects of dietary macronutrient composition and energy intake on β-cell physiology and glucose homeostasis. It has been further established that obesity is a leading pathogenic factor for developing insulin resistance. However, insulin resistance may not progress to T2D unless β-cells are unable to secret an adequate amount of insulin to compensate for decreased insulin sensitivity. Therefore, pancreatic β-cell dysfunction plays an important role in the development of overt diabetes. This paper reviews recent research findings on the effects of several micronutrients (zinc, vitamin D, iron, vitamin A), leucine, and the phytochemical, genistein on pancreatic β-cell physiology with emphasis on their effects on insulin secretion, specifically in the context of T2D.

Vitamin D Deficiency and Cardiometabolic Risks: A Juxtaposition of Arab Adolescents and Adults

The recent exponential surge in vitamin D research reflects the global epidemic of vitamin D deficiency and its potential impact on several chronic diseases in both children and adults. Several subpopulations, including Arab adolescent boys and girls, remain understudied. This study aims to fill this gap. A total of 2225 apparently healthy Saudi adolescents (1187 boys and 1038 girls, aged 13-17 years old) and 830 adults (368 men and 462 women, aged 18-50 years old) were respectively recruited from different public schools and medical practices within Riyadh, Saudi Arabia. Anthropometrics were taken and fasting blood samples withdrawn to examine serum glucose and lipid profile by routine analysis and 25-hydroxyvitamin D by ELISA. Almost half of the girls (47.0%) had vitamin D deficiency as compared to only 19.4% of the boys (p<0.001), 36.8% of the adult women and 17.7% of the adult men (p<0.001). Furthermore, in boys there were more significant inverse associations between serum 25(OH)vitamin D levels and cardiometabolic indices than girls, while in contrast women had more significant associations than men. Vitamin D deficiency was significantly associated with diabetes mellitus type 2 (DMT2) [OR 3.47 (CI1.26-5.55); p<0.05] and pre-DM [OR 2.47 (CI 1.48-4.12); p<0.01] in boys. Furthermore, vitamin D insufficiency was significantly associated with abdominal obesity in boys [OR 2.75 (CI 1.1-7.1); p<0.05]. These associations for DMT2 and abdominal obesity were not observed in adult males, girls and adult women. Vitamin D deficiency/insufficiency and hyperglycemia is high among Arab adolescents. Vitamin D deficiency is mostly associated with cardiometabolic risk factors in adolescent Arab boys. This indicates a sex- and age-related disadvantage for boys with low vitamin D status and challenges the extra-skeletal protection of vitamin D correction in adolescent females.

Vitamin D intake associates with insulin resistance in type 2 diabetes, but not in latent autoimmune diabetes in adults

This study aimed to evaluate the relationship between vitamin D (vitD) intake and serum concentrations and insulin secretion (assessed by C-peptide serum concentration)/insulin resistance (determined by estimated glucose disposal rate [eGDR]) in patients with latent autoimmune diabetes in adults (LADA) and type 2 diabetes (T2DM). C-peptide, serum vitD, lipid profile, insulin, glucose, and glycosylated hemoglobin (HbA1c) were assessed; vitD intake was determined; and eGDR was calculated. Groups were compared using the Student t or Mann-Whitney U test. Correlations were performed between insulin secretion, insulin resistance, and vitD, and linear regression models were adjusted for confounding variables. Of 107 patients included, age was 55.3 ± 11.84 years old, and time since diabetes diagnosis was 13.23 ± 5.96 years. There were significant intergroup differences in age, body mass index (BMI), hip measurements, glucose, and HbA1c. The correlation between vitD intake and C-peptide for the whole group was significant (r = 0.213; P = .032) as well as for vitD deficiency/sufficiency in T2DM (P = .042), whereas neither was significant in eGDR. After adjustment for age, HbA1c, disease progression, physical activity, solar exposure, sex, and BMI, vitD intake was only significant in T2DM (P = .028). In serum vitD, only the correlation between eGDR and vitD in T2DM was significant and intragroup when comparing vitD sufficiency. After adjustments, significance was lost. Patients with LADA had lower intake of vitD, poorer metabolic control, lower BMI, and younger age compared to T2DM patients. There was no association between serum vitD or vitD intake and insulin secretion when analyzed by group, although vitD intake was associated with insulin resistance in T2DM, but not LADA.

No association between 25-hydroxyvitamin D levels and prediabetes in Brazilian patients. A cross-sectional study

CONTEXT AND OBJECTIVE

Several studies have evaluated the role of low 25-hydroxyvitamin D (25OHD3) in the pathogenesis of type 2 diabetes (T2DM) and have presented controversial results. The metabolic processes that culminate in T2DM begin under prediabetic conditions. Our aim was to analyze the association between 25OHD3 and glucose metabolism in individuals who were free from but at elevated risk of diabetes.

DESIGN AND SETTING

Cross-sectional study at a tertiary hospital.

METHODS

Anthropometric and laboratory profiles were determined in patients with one or more of the following risk factors: hypertension; body mass index (BMI) ≥ 25 kg/m2; waist circumference > 80 cm for women and > 94 cm for men; first-degree relatives with diabetes; women with large-for-gestational-age newborns or with gestational T2DM; HDL-cholesterol (high density lipoprotein) < 35 mg/dl; and triglycerides > 250 mg/dl. The patients were divided into two groups: one with prediabetes (abnormal fasting plasma glucose or oral glucose tolerance test) and the other with normal glucose (euglycemic).

RESULTS

There was no statistically significant difference between the prediabetic group (n = 38) and euglycemic group (n = 15) regarding age (66.4 ± 10.6 versus 62.6 ± 9.1 years), gender (52.6 versus 73.3% female) and BMI (30.1 ± 4.61 versus 27.9 ± 4.7 kg/m2). Low serum levels of 25OHD3 were found in both groups, without any statistically significant difference between them (29.1 ± 11.8 versus 26.87 ± 9.2 ng/dl).

CONCLUSION

There was no association between 25OHD3 levels and the clinical or laboratorial variables analyzed.

Relationship of vitamin D with insulin resistance and disease severity in non-alcoholic steatohepatitis

BACKGROUND & AIMS

The role of plasma vitamin D deficiency in the development of non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH) remains poorly understood. Previous studies have suggested a role for vitamin D deficiency in the pathogenesis of NAFLD/NASH, but they have been rather small, and/or NAFLD was diagnosed using only aminotransferases or liver ultrasound. This study aimed to assess the role of vitamin D deficiency in relationship to liver fat accumulation and severity of NASH.

METHODS

A total of 239 patients were recruited and state-of-the-art techniques were used to measure insulin resistance (euglycemic insulin clamp with 3-(3)H-glucose), liver fat accumulation (magnetic resonance spectroscopy or (1)H-MRS), total body fat (dual energy X-ray absorptiometry), and severity of liver disease (liver biopsy).

RESULTS

Patients were divided into 3 groups according to plasma 25-hydroxyvitamin D levels (normal: >30 ng/ml; insufficiency: 20-30 ng/ml; deficiency: <20 ng/ml). When well-matched for clinical parameters (BMI, total adiposity, or prevalence of prediabetes/type 2 diabetes), no significant differences were observed among groups in terms of skeletal muscle, hepatic, or adipose tissue insulin sensitivity, the amount of liver fat by (1)H-MRS, or the severity of histological inflammation, ballooning, or fibrosis. Patients were then divided according to liver histology into those with definite NASH and those without NASH. Although patients with NASH had higher insulin resistance, plasma vitamin D concentrations were similar between both groups.

CONCLUSIONS

Our results suggest that plasma vitamin D levels are not associated with insulin resistance, the amount of liver fat accumulation, or the severity of NASH.

Cholecalciferol supplementation does not influence β-cell function and insulin action in obese adolescents: a prospective double-blind randomized trial

BACKGROUND

There is increasing interest in the extraskeletal effects of vitamin D, particularly in the obese state with regard to the development of insulin resistance and diabetes.

OBJECTIVE

The objective of the study was to determine the effect of 2 doses of cholecalciferol (vitamin D3) supplementation on insulin action (Si) and pancreatic β-cell function in obese adolescents.

METHODS

We performed a 12-wk double-blind, randomized comparison of the effect of vitamin D3 supplementation on Si and β-cell function in obese Caucasian adolescents (body mass index > 95(th) percentile). The subjects were randomly assigned to receive either 400 IU/d (n = 25) or 2000 IU/d (n = 26) of vitamin D3. Each subject underwent a 7-sample 75 g oral glucose tolerance test, with glucose, insulin, and C-peptide measurements, to calculate Si and β-cell function as assessed by the disposition index (DI), with use of the oral minimal model before and after supplementation. A total of 51 subjects aged 15.0 ± 1.9 y were enrolled. Included for analysis at follow-up were a total of 46 subjects (20 male and 26 female adolescents), 23 in each group.

RESULTS

Initial serum 25-hydroxyvitamin D [25(OH)D] was 24.0 ± 8.1 μg/L. There was no correlation between 25(OH)D concentrations and Si or DI. There was a modest but significant increase in 25(OH)D concentration in the 2000 IU/d group (3.1 ± 6.5 μg/L, P = 0.04) but not in the 400 IU/d group (P = 0.39). There was no change in Si or DI following vitamin D3 supplementation in either of the treatment groups (all P > 0.10).

CONCLUSIONS

The current study shows no effect from vitamin D3 supplementation, irrespective of its dose, on β-cell function or insulin action in obese nondiabetic adolescents with relatively good vitamin D status. Whether obese adolescents with vitamin D deficiency and impaired glucose metabolism would respond differently to vitamin D3 supplementation remains unclear and warrants further studies. This trial was registered at clinicaltrials.gov as NCT00858247.

The status of 25-hydroxyvitamin D across the spectrum of glucose tolerance among middle-aged and elderly Chinese individuals

CONTEXT

Although vitamin D status and its inverse association with diabetes among White people have been recognized, little research on vitamin D status has been well conducted in Chinese individuals based on glucose tolerance.

OBJECTIVE

To compare the vitamin D status of Chinese individuals aged 40-75 years based on the glucose tolerance status.

DESIGN AND METHODS

Serum 25OHD was measured in a cross-sectional sample of 10 038 individuals aged 40-75 years from Lanzhou city, which is located in western China.

RESULTS

People with normal glucose tolerance (NGT, n = 4744), prediabetes (n = 2808) or diabetes (n = 2486) aged 40-75 years were included in the study. The difference in 25OHD concentration between people with NGT and prediabetes was not significant (16·5 vs 16·0 ng/ml, P = 0·773), but the 25OHD concentration of diabetes was higher than that of subjects with NGT (16·5 vs 16·5 ng/ml, P = 0·025) and prediabetes (16·5 vs 16·0 ng/ml, P = 0·032) after adjusting confounders. There was no difference in the prevalence of vitamin D deficiency between people with NGT and diabetes (74·7% vs 74·0%, P = 0·535), but the prevalence of vitamin D deficiency of prediabetes was higher than that of people with NGT (77·0% vs 74·7%, P = 0·024) and diabetes (77·0% vs 74·0%, P = 0·012).

CONCLUSIONS

Although vitamin D status was significantly different across the spectrum of glucose tolerance in middle-aged and elderly Chinese individuals, the difference was not clinically significant. The results, however, highlight the very high prevalence of vitamin D deficiency in this population and should raise the awareness of this important public health issue among health-care providers.

Vitamin D insufficiency and insulin resistance in obese adolescents

Obese adolescents represent a particularly vulnerable group for vitamin D deficiency which appears to have negative consequences on insulin resistance and glucose homeostasis. Poor vitamin D status is also associated with future risk of type 2 diabetes and metabolic syndrome in the obese. The biological mechanisms by which vitamin D influences glycemic control in obesity are not well understood, but are thought to involve enhancement of peripheral/hepatic uptake of glucose, attenuation of inflammation and/or regulation of insulin synthesis/secretion by pancreatic β cells. Related to the latter, recent data suggest that the active form of vitamin, 1,25-dihydroxyvitamin D, does not impact insulin release in healthy pancreatic islets; instead they require an environmental stressor such as inflammation or vitamin D deficiency to see an effect. To date, a number of observational studies exploring the relationship between the vitamin D status of obese adolescents and markers of glucose homeostasis have been published. Most, although not all, show significant associations between circulating 25-hydroxyvitamn D concentrations and insulin sensitivity/resistance indices. In interpreting the collective findings of these reports, significant considerations surface including the effects of pubertal status, vitamin D status, influence of parathyroid hormone status and the presence of nonalcoholic fatty liver disease. The few published clinical trials using vitamin D supplementation to improve insulin resistance and impaired glucose tolerance in obese adolescents have yielded beneficial effects. However, there is a need for more randomized controlled trials. Future investigations should involve larger sample sizes of obese adolescents with documented vitamin D deficiency, and careful selection of the dose, dosing regimen and achievement of target 25-hydroxyvitamn D serum concentrations. These trials should also include clamp-derived measures of in vivo sensitivity and β-cell function to more fully characterize the effects of vitamin D replenishment on insulin resistance.

Prospective associations of vitamin D status with β-cell function, insulin sensitivity, and glycemia: the impact of parathyroid hormone status

Previous studies have yielded conflicting findings on the relationship between low vitamin D (25-OH-D) and impaired glucose homeostasis. In this context, we hypothesized that combined assessment of 25-OH-D with its regulator parathyroid hormone (PTH) may be required for optimal evaluation of the impact of vitamin D status on glucose metabolism. Thus, we evaluated the prospective associations of 25-OH-D and PTH at 3 months postpartum with β-cell function (Insulin Secretion-Sensitivity Index-2 [ISSI-2]), insulin sensitivity (Matsuda index), and glycemia at 12 months postpartum in 494 women undergoing serial metabolic characterization. Notably, 32% of those with prediabetes/diabetes mellitus at 12 months postpartum had both vitamin D deficiency and PTH in the highest tertile at 3 months postpartum. On multiple-adjusted linear regression analyses, vitamin D deficiency/insufficiency with PTH in the highest tertile at 3 months independently predicted poorer β-cell function (P = 0.03) and insulin sensitivity (P = 0.01) and increased fasting (P = 0.03) and 2-h glucose (P = 0.002) at 12 months postpartum. In contrast, vitamin D deficiency/insufficiency with lower PTH did not predict these outcomes. In conclusion, only vitamin D deficiency/insufficiency with increased PTH is an independent predictor of β-cell dysfunction, insulin resistance, and glycemia, highlighting the need for consideration of the PTH/25-OH-D axis when studying the impact of vitamin D status on glucose homeostasis.

National report on the association of serum vitamin D with cardiometabolic risk factors in the pediatric population of the Middle East and North Africa (MENA): the CASPIAN-III Study

OBJECTIVES

As the first, to our knowledge, nationwide study in the Middle East and North Africa (MENA), this study aimed to investigate the association of serum 25 hydroxy vitamin D [25(OH)D] levels with cardiometabolic risk factors in a nationally representative sample of the pediatric population in Iran. The second objective was to provide the prevalence of hypovitaminosis D and the percentiles of serum 25(OH)D in the study population.

METHODS

This national population-based study was conducted among 1100 Iranian students living in 27 provinces in Iran. The association of 25(OH)D with each cardiometabolic risk factor was determined after adjustment for age, gender, body mass index, and waist circumference.

RESULTS

Participants consisted of 1095 students (52% boys) with a mean age of 14.74 ± 2.61 y. The median 25(OH)D level corresponded to a vitamin D insufficiency level: 12.70 ng/mL in boys and 13.20 ng/mL in girls. Overall, 40% of participants were vitamin D deficient, and 39% had vitamin D insufficiency. There were no significant differences in these findings between boys and girls. Adjusted regression analysis revealed a significant weak inverse association of 25(OH)D with systolic blood pressure, diastolic blood pressure, total cholesterol, and low-density lipoprotein cholesterol. This association was significantly positive with high-density lipoprotein cholesterol, but not with fasting plasma glucose and metabolic syndrome.

CONCLUSION

We found a considerably high prevalence of hypovitaminosis D in the pediatric population of a sunny region. Our findings also revealed an association of hypovitaminosis D with many cardiometabolic risk factors from childhood; these associations were independent of obesity indexes. It is of special concern that the highly prevalent disorders of low 25(OH)D and low high-density lipoprotein cholesterol in children and adolescents of the MENA region had significant association. The clinical importance of our findings needs to be confirmed in longitudinal studies.

Vitamin D and 1-hour post-load plasma glucose in hypertensive patients

Background

A plasma glucose value ≥155 mg/dl for 1-hour post-load plasma glucose during an oral glucose tolerance test (OGTT) is able to identify subjects with normal glucose tolerance (NGT) at high-risk for type-2 diabetes and with subclinical organ damage. We designed this study to address if 25-hydroxyvitamin D [25(OH)D] circulating levels are associated with glucose tolerance status, and in particular with 1-hour post-load plasma glucose levels.

Methods

We enrolled 300 consecutive Caucasian hypertensive never-treated outpatients (160 men and 140 women, aged 52.9 ± 9.2 years). Subjects underwent OGTT and measurements of 25(OH)D and standard laboratory tests. Estimated glomerular filtration rate (e-GFR) was calculated by CKD-EPI formula and insulin sensitivity was assessed by Matsuda-index.

Results

Among participants, 230 were NGT, 44 had impaired glucose tolerance (IGT) and 26 had type-2 diabetes. According to 1-h post-load plasma glucose cut-off point of 155 mg/dL, we divided NGT subjects into: NGT < 155 (n = 156) and NGT > 155 mg/dL (n = 74).

NGT ≥ 155 had higher significant fasting and post-load glucose and insulin, parathyroid hormone and hs-CRP levels than NGT < 155. On the contrary, Matsuda-index, e-GFR, and 25(OH)D were significantly lower in NGT ≥ 155 than NGT < 155 subjects. In the multiple regression analysis, 25(OH)D levels resulted the major determinant of 1-h post-load plasma glucose in all population and in the four groups of glucose tolerance status. In the whole population, Matsuda-index, hs-CRP and e-GFR explained another 12.2%, 6.7% and 1.7% of its variation.

Conclusions

Our data demonstrate a significant and inverse relationship between 25(OH)D levels and glucose tolerance status, particularly with 1-h post-load glucose.

Association between nontraditional risk factors and metabolic syndrome in indigenous Argentinean schoolchildren

BACKGROUND

Whether apolipoproteins (Apos) are better cardiovascular disease (CVD) markers than metabolic syndrome (MS) is widely debated. Measurement of Apo B is standardized, simple, and inexpensive and does not require fasting. The aim of this study was to compare the ability of nontraditional CVD markers such as Apo B, Apo B/Apo A, non-high-density lipoprotein cholesterol (HDL-C), vitamin D, and homeostasis model assessment of insulin resistance (HOMA-IR) to identify children with MS.

SUBJECTS AND METHODS

A cross-sectional study of 355 Argentinean Koya schoolchildren (166 boys) 9.6±2.3 years old was performed in November 2011. Anthropometric measures, blood pressure, Tanner stages, and serum levels of glucose, lipids, insulin, Apo A, Apo B, and vitamin D were measured.

RESULTS

The prevalence of overweight/obesity was 10.7% (n=38), and that of underweight was 14.6% (n=52) using Centers for Disease Control and Prevention criteria. The prevalence of central obesity was 10.9% (38/355), high triglycerides was 11.1% (39/355), low HDL-C was 44.9% (158/355), hypertension was 12.8% (45/355), hyperglycemia was 0.3% (1/355), and MS was 4.2% (15/355). Several multiple logistic regression analyses showed that MS was significantly associated with HOMA-IR (odds ratio [OR], 3.6 [95% confidence interval (CI) 1.51-8.52]), non-HDL-C (OR, 1.03 [95% CI 1.007-1.049]), Apo B (OR, 1.06 [95% CI 1.03-1.09]), and Apo B/Apo A (OR, 78.3 [95% CI 3.67-1,674.4]) adjusted for age and gender. Furthermore, the areas under the receiver operator characteristic curves were as follows: Apo B, 0.77 (95% CI 0.63-0.90); Apo B/Apo A, 0.76 (95% CI 0.63-0.88); non-HDL-C, 0.72 (95% CI 0.57-0.85); and HOMA-IR, 0.69 (95% CI 0.49-0.90). These values indicate that these variables were acceptable predictors for MS.

CONCLUSIONS

This is the first study of nontraditional markers in South American Indian children. MS was associated with multiple nontraditional markers of future CVD risk such as non-HDL-C, Apo B, and Apo B/Apo A. However, Apo B was the best predictor for MS, suggesting that it could be used as a risk marker of future CVD in this community.

[High prevalence of vitamin D deficiency among spanish obese children and adolescents]

INTRODUCTION

Vitamin D deficiency has been associated with extra-skeletal outcomes such as, insulin resistance, type 2 diabetes, and cardiovascular disease. The aim of this study is to determine the prevalence of vitamin D deficiency among obese children and adolescents in Spain and to analyze the relationship between 25-OH-vitamin D (25-OH-D) levels and markers of abnormal glucose metabolism.

PATIENTS AND METHODS

A cross-sectional study was conducted in which the clinical and biochemical data were recorded for 120 obese and 50 non-overweight children in Pediatric Clinics from January 2011 to January 2013.

RESULTS

The mean 25-OH-D levels among obese children was 19.5 ng/ml and among non-overweight children was 31.6 ng/ml. 58,3% of obese subjects, and 10% of non-overweight subjects had vitamin D deficiency. Serum 25-OH-D levels were lower in winter. Higher HOMA-SDS (3.8 versus 2.4), and triglycerides (97 versus 81 mg/dl) were found in vitamin D deficient obese children compared to obese children without vitamin D deficiency. A negative correlation was found between 25-OH-D levels and HOMA in absolute values (r=-0.2; P=.04) that was not maintained when HOMA-SDS was analyzed.

CONCLUSIONS

There is a high prevalence of vitamin D deficiency among obese children with a multifactorial etiology. A lower 25-OH-D level could be a risk factor for developing insulin resistance and type 2 diabetes in obese population.

Vitamin D deficiency in childhood obesity is associated with high levels of circulating inflammatory mediators, and low insulin sensitivity

HYPOTHESIS

Childhood obesity is accompanied by low-grade systemic inflammation, which contributes to the development of insulin resistance and cardiovascular complications later in life. As vitamin D exhibits profound immunomodulatory functions and vitamin D deficiency is highly prevalent in childhood obesity, we hypothesized that vitamin D deficiency in childhood obesity coincides with enhanced systemic inflammation and reduced insulin sensitivity.

METHODS

In a cross-sectional study of 64 obese and 32 healthy children aged 6-16 years, comprehensive profiling of 32 circulating inflammatory mediators was performed, together with assessment of 25-hydroxyvitamin D (25(OH)D) levels and measures for insulin sensitivity.

RESULTS

Severe vitamin D insufficiency, which is further referred to as vitamin D deficiency, was defined as a 25(OH)D level ≤37.5 nmol l(-1), and was highly prevalent in obese (56%) versus healthy control children (16%). Throughout the study, 25(OH)D-deficient children were compared with the other children, including 25(OH)D insufficient (37.5-50 nmol l(-1)) and 25(OH)D sufficient children (≥50 nmol l(-1)). First, 25(OH)D-deficient obese children showed a lower insulin sensitivity than other obese children, as measured by a lower quantitative insulin sensitivity check index. Second, the association between 25(OH)D deficiency and insulin resistance in childhood obesity was confirmed with multiple regression analysis. Third, 25(OH)D-deficient obese children showed higher levels of the inflammatory mediators cathepsin S, chemerin and soluble vascular adhesion molecule (sVCAM), compared with the other obese children. Finally, hierarchical cluster analysis revealed an over-representation of 25(OH)D deficiency in obese children expressing inflammatory mediator clusters with high levels of cathepsin S, sVCAM and chemerin.

CONCLUSION

25(OH)D deficiency in childhood obesity was associated with enhanced systemic inflammation and reduced insulin sensitivity. The high cathepsin S and sVCAM levels may reflect activation of a pro-inflammatory, pro-diabetic and atherogenic pathway, which could be inhibited by vitamin D supplementation.